Question

I’am wondering if built-in types in objects created on heap with new will be initialized to zero? Is it mandated by the standard or is it compiler specific?

Given the following code:

#include <iostream>

using namespace std;

struct test
{
    int _tab[1024];
};

int main()
{
    test *p(new test);

    for (int i = 0; i < 1024; i++)
    {
        cout << p->_tab[i] << endl;
    }

    delete p;
    return 0;
}

When run, it prints all zeros.

Answer 1

No, if you do something like this:

int *p = new int;

or

char *p = new char[20];  // array of 20 bytes

or

struct Point { int x; int y; };
Point *p = new Point;

then the memory pointed to by p will have indeterminate/uninitialized values.

However, if you do something like this:

std::string *pstring = new std::string();

Then you can be assured that the string will have been initialized as an empty string, but that is because of how class constructors work, not because of any guarantees about heap allocation.